1. Field of the Invention
The present invention relates to a rotation-body controlling apparatus including an origin-position detecting portion for detecting an origin position of a rotation phase of a rotation body without upsizing of the apparatus and increase in cost, a sheet feeding apparatus including the rotation-body controlling apparatus, and an image recording apparatus configured to record a non-distorted beautiful image on a sheet.
2. Description of the Related Art
A printer and a scanner include a sheet feeding apparatus for feeding a sheet such as a document. The sheet feeding apparatus includes a roller driven to be rotated in a state in which the roller is held in contact with the sheet. In order to record a non-distorted beautiful image on a recording sheet, and to realize image reading of a document with high image quality, the sheet is fed by receiving a rotational force of this roller. There is a need to accurately control a feeding amount of the sheet. However, in the sheet feeding apparatus, a rotation amount of the roller may not be accurately controlled because of an error of mounting of a sensor for detecting the rotation amount of the roller, an error of attachment of a gear to the roller, and so on. Further, even where the rotation amount of the roller is accurately controlled, feeding of the sheet may not be even because of an error of manufacturing of the roller. Thus, in the sheet feeding apparatus, the feeding amount of the sheet is periodically changed because of these errors. In a conventional sheet feeding apparatus, there is provided a means for correcting the feeding amount of the sheet by detecting the periodical change of the feeding amount of the sheet (for example, with reference to Patent Documents 1-4).
An ink-jet recording apparatus disclosed in Patent Document 3 (JP-A-2006-224380) records an image on a sheet while correcting a rotation amount of a roller on the basis of a result of detection of the rotation amount of the roller by a rotary encoder. Where the rotation amount of the roller is preferably corrected, a pattern whose concentration change is small is recorded on the sheet. In contrast, where the rotation amount of the roller is not appropriately corrected, a pattern whose concentration change is large is recorded on the sheet. In the ink-jet recording apparatus, a plurality of patterns are recorded on the sheet while changing an amount of correction of the rotation amount of the roller, and then a correction value of the rotation amount of the roller in one of the patterns whose evenness in the concentration is the smallest is obtained and stored into a memory. Then, the rotation amount of the roller is corrected on the basis of this correction value.
Patent Document 1 (JP-A-10-38902) discloses a means for eliminating an effect of an eccentricity of an encoder disc from a rotation speed of a roller which has been detected by a rotary encoder. A rotation-speed detecting device disclosed in this document includes a phase detecting rotational circular disc and an optical sensor. The phase detecting rotational circular disc is a disc on which one light detecting area is provided, and fixed to a rotation shaft of the roller with the encoder disc. The optical sensor includes a light emitting element and a light receiving element which are disposed so as to be opposed to each other at a predetermined distance with an outer edge of the phase detecting rotational circular disc interposed therebetween. One pulse signal is outputted from the optical sensor in each rotation of the roller, and an origin position of the rotation shaft of the roller is identified on the basis of this pulse signal. The periodical change of the feeding amount of the sheet which is generated with one rotation of the roller being as one cycle is grasped on the basis of the origin position, and the rotation of the roller is controlled such that the periodical change is balanced out.
A rotation controlling apparatus disclosed in Patent Document 2 (U.S. Pat. No. 7,060,969 B2 corresponding to JP-A-2005-168280) includes three rotation sensors for detecting a rotation of a rotary encoder. Each of the rotation sensors includes a light emitting element and a light receiving element which are disposed so as to be opposed to each other with a predetermined space interposed therebetween. An encoder disc of each rotary encoder is fixed to an output shaft of a motor. Each rotation sensor is disposed such that an outer edge of the encoder disc is located in the space, and is arranged at a right angle with respect to a circumferential direction of the encoder disc. In the rotation controlling apparatus, a rotation speed of the output shaft of the motor is calculated by performing a predetermined computing processing for an output signal outputted from each rotation sensor. Then, a rotation of the motor is controlled such that the rotation speed coincides with a target rotation speed.
In a sheet feeding apparatus disclosed in Patent Document 4 (JP-A-2007-197186), a target rotation amount of a sheet-feed roller is corrected on the basis of a correction value obtained by a computation, whereby a periodic deviation of a rotation amount of the sheet-feed roller is balanced out. Further, in this sheet feeding apparatus, a current rotation phase of the sheet-feed roller is determined with a position of the sheet-feed roller at a time when a constant-speed rotation of the sheet-feed roller is finished being as a reference position. Then, where the sheet-feed roller is rotated, the current rotation phase of the sheet-feed roller is updated in accordance with the rotation amount of the sheet-feed roller with respect to the reference position.